JavaScriptArrays

Array.isArray()

Checks whether a value is an array.

On this page

Example

JavaScript

console.log(Array.isArray([1, 2]))
console.log(Array.isArray({ length: 2 }))
console.log(Array.isArray('text'))
console.log(typeof [1, 2])

Console

true

false

object

The static Array.isArray() method returns true if the given value is an array, and false in every other case.

It’s needed because the typeof operator returns "object" for arrays, just like for plain objects and null. You can’t tell them apart that way.

It comes in handy with data from outside the app, for example from an API or a JSON file, where a field might be a single value or a list.

Array.isArray(value)

Parameter	Type	Description
value	any value	The value to check.

Normalizing data

JavaScript

const toList = (value) => (Array.isArray(value) ? value : [value])

console.log(toList('HTML'))
console.log(toList(['HTML', 'CSS']))

Console

['HTML']

['HTML', 'CSS']

Widely available

Works in all modern browsers, phones included. You can use it without worry.

Don’t check for arrays with typeof. It always returns "object".
A function that turns a single value into an array (toList) simplifies handling data from forms and APIs.

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